Telephone system



Jan; 28, 1930.v `.1. E. osTuNE 1,745,037

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'TELEPHONE SYSTEM Filed sept. 28, 1927 e sheets-sheet 2 pur CIO

Jan. 28, 1930. J. E. osTL'xNl-z 1,745,037

TELEPHONE SYSTEM Filed sept.- 28. 192'/ s sheets-sheet 3 J. E. osTLlNE1,745,037

ATELEPHONE: SYSTEM Filed Sept. 28. 1927 6 Sheets-Sheet 4 y 1m28, 1930;l

J. E. osTLlNE y 1,745,037 TELEPHONE SYSTEI Filed sept. 28, 1927 esheets-sheet s.

`Imran 1:111-` Jamin-511mg Jan. 28, 1930. J, E- QSTLINE 1,745,037

TELEPHONE SYSTEM Filed sep't. 28, 1927 e sheets-snee@ 6 Patented Jan.28, 1930 unirse STATESr `JOHN ELLIS OSTLINE, or Livnnroon, ENGLAND,ASSIGNOR To ASSOCIATED TELE- PHONE AND TELEGRAPH CoM-PANY, or KANSASCITY,

0F DELAWARE Application led September 28, 1%327, Serial No.

The present invention relates to telephone systems and is moreparticularly concerned with what-is known as routine testing apparatus,that is to say apparatus arranged'to reproduce automatically .the actualconditions ofV use for each unit in turn of a large group of similarpieces ofi apparatus. Moreover the invention while not definitelyrlimited thereto is more specially applicable to the testing ofso-called first code selectors which may be broadly defined as firstynumerical switches in a System employing register controllers. In :sucha system a first code selector is taken into use over an individual lineswitch when a subscriber calls and thereupon temporarily associates withitself a' register controller adapted to respond to thek impulsesdialled by the calling party. In due course the register controllersends out corresponding trains of impulses, the first series serving vtooperate the first code selector, and-when the connection has beencompletely set kup the register controller is released. Such a firstcode selector, is therefore considerably more complicated than a simpleselector switch, and the routine tests ymust include some arrangementsfor testing also the apparatus for associating the register controllerwith the connection. It is the object of the Yinvention to produceroutine testing equipment which shall satisfactorily perform*y all thefunctions outlined above, though it will be understood that certain ofthe lprinciples involved can equally well be applied to the Vtesting ofotherliinds of apparatus.

The testing equipment mayy conveniently be divided into two parts,firstly the testing apparatus proper, and secondly the distribe utingswitches by means of whichthe testing apparatus is associated withktheparticular piece' of apparatus it is desired to'. test. In somecircumstances it may be desirable to provide facilities for testing theapparatus' manually as well as automatically, and in suoli a case it ispreferablev to employ the same distributing equipment for connectingwith both the manual and automatic testing equip-y ment. According toone feature.v of the invention therefore, the various pieces ofapparatus are adapted to be associated in turn PATENT OFFICE `MISSOURI,A CORPORATION TELEPHONE SYSTEM 222,456, and in Great Britain October 14,1926.

with automatic testing apparatus over distributing switches, while meansare also provided whereby the pieces of apparatus may also be associatedyover 'the 'distributing switches with manual testing equipment.

In 'systems of the kind referredto, inasmuch as register controllersshould normally provided for releasing a register controller in case 1tbecomes associatedV with` a line butv is not used, as may be broughtabout for instance by a fault on the line. According to another featureof the invention, therefore, in a testing arrangement for the routinetesting of apparatus arranged to effect the temporary association ofother apparatus therewith, which otherapparatus isr arranged to beautomatically released if held for more than a predetermined time, oneof the tests consists in the seizing and holding of a piece of apparatussuiiiciently long to test the forcedrelease feature. I

A further vfeature of the invention is that in a testing arrangement forthe routine testing of apparatus which is equally available from theroutining equipment and from its normal means of access, when aparticular piece of apparatus -is to be completely rou:-

tined a plurality of times in succession, :spe-

signed to test first code selectors of the type described in'BritishPatent No. 264,557,7but4 it will be understood that it is 'not limitedto use with iirst code selectors' of this type since the principlesinvolved are capable of con-v siderably wider application.

In a 10,000 line exchange, for which the routiner about to be describedis intended to serve, there will probably be from 1,000 to 1,500 firstcode selectors, and in accordance with the usual practice these will bearranged in shelves each containing switches. For convenience in cablingit is desirable that access should be obtained from one particularswitch to the 20 switches comprising a shelt. Conveniently therefore thedistributing arrangements comprise a number of secondary distributorsequal to the number of shelves of first code selectors and a number ofprimary distributors sufficient to give access to all the secondarydistributors. Preferably also the primary distributors are arranged tobe con nected in tandem over their th contacts, that is to say the firstprimary distributor will have its wipers directly associated with theroutining equipment and the first 2st contacts in its bank will extendto secondary distributors. The 25th set of contacts however will extendto the wipers of the succeeding primary distributor which is wired in asimilar manner. The switches associated with the first code selectorsfor selecting an idle register controller, sometimes known as A digitselectors, are preferably of the homing type and the contacts engaged bythe line and pulsing wipers in normal position are wired to the routinerand are made use of in carrying out manual tests as will be describedsubsequently. For the sake of convenience there is provided on eachfirst code selector board a 10-point ack connected through to theroutiner. All these jacks are multiplied together and any one can beused for effecting manual tests so that it is possible for the attendantto carry out tests from a position in which he can observe the actualoperation of the first code selector. A connection also extends back tothe routiner from a vacant level in an exchange selector and over thisline circuit changes may be effected corresponding to the reply of acalled party.

Referring to the drawings, Fig. 1 shows three eight level primarydistributor switches, S1171, SW2, SW3, and one secondary six leveldistributor switch SW".

Fig. 2 shows the fault indicating lamps FL, together with lamps BSL forindicating the bay and shelf of a particular switch being routined andswitch lamps SL which indicate the particular switch under test. Thisfigure also shows the control keys and two time check relays TC1 andTG2.

Fig. 3 shows the routiner impulse sending switch SS, together with thevibrator V employed for generating impulses.

Fig. 4: shows the release timing switch RT which is employed to checkthe time of release of the switches under test.

Fig. 5 shows the test control switch TC which controls the tests appliedto the various switches.

Fig. 6 shows the test switch TS which is employed for altering theconnections of the various conductors extending by way of' thedistributor switches from the switch under test.

In the arrangement shown in Fig. 1, access may be had to as many as 1440first code switches. The primary distributors S1171, SW2 and SVS/'3 are25 point switches, and each have access to 24 secondary distributors,while the secondary distributors each have access to 20 first codeswitches. All the switches SW1, S1172, S1173, S1V4, SS, RT, TC and TSare of the homing type and advance their wipers one step on release oftheir operating magnets.

A description will be first given of a successful routine test of agroup of first code selectors. In order to set the routine apparatusshown in operation, the exchange attendant operates the automaticroutine start key AS, Fig. 2, which completes the following circuit forstart relay ST, Fig. 3-battery, relay ST, conductor 10, cable C1,conductor l0, start key spring AS1, to earth. The start key AS also setsa time pulse mechanism (not shown) in operation, which is arranged toconnect impulses at the rate of 40 per minute (.75 seconds on and .75seconds off) to conductor PC1, Fig. 6; 20 impulses per minute at therate of 1 second on and 2 seconds off, to conductor PC2, and 20 persecond continuous to conductor FC3. At ST2 and ST3, relay ST prepares atesting circuit, which extends from battery, upper winding of relay TT,Fig. 6, normally closed contacts controlled by armature TLZ, conductor11, cable C4, conductor 11, Fig. 2, junction testkey springs 4,resistance r1 junction test key springs 2, conductor 12, cable C1,conductor 13, ST2, negative terminal 14, which with its associatedpositive terminal 15 is connected to a spare level of an exchangeselector. The positive terminal 15 extends over springs ST3, conductor18, cable C1, conductor 18, junction test key springs 1, resistance 112,resistance 1'1", cable C1, conductor 18, Fig. 6, normally closedcontacts controlled by armature TR1, lower winding of relay TT,conductor 19. cable C22, conductor 19, Fig. 5, armature TG5 to earth.Relay ST at ST4 prepares a circuit for testing whether the switch isengaged or its position on the shelf unequipped, by connecting earth toconductor 20, cable C17, conductor 20, resistance R1, R2, battery. RelayST at ST5 prepares a circuit for two-step relay DS; at ST6 prepares acircuit for the driving magnet DH1 of the primary distributor switchS1171, Fig. 1; at ST7 connects earth impulses at the rate of 40 perminute to relay DQ over the circuit; pulse conductor PC1, Fig. 6, cableC23, conductor 22, PM1, conductor 23, cable C1, conductor 23, ST7,conductor 24, DQ1, conductor 24, DB1, conductor 25, lower windingSS3,`SS4, SS5 and SS6 disconnects the h-oming circuits for the primarydistributors SVP, SW2 and SW3, at SS7 completes the following circuitfor relays HA and HB; earth, SS?, conductor 26, cable C16, conductor 26,relay HA and relay HB in parallel to battery, and at SS8 prepares acircuit for relay DE, which will be described later.

The next pulse over conductor P01 operates relay DR, Fig. 3 as follows:relay DR, conductor 27, DQ1, conductor 24, ST7 and the previously tracedcircuit to pulse conductor PS1, Fig. 6. Relay DR completes aI circuitfor relay DS as follows: earth, DB1, conductor 28, ST5, conductor 29.DS1, conductor 30, lower winding ofrelay DS to battery. Relay DS is atwo-step relay, and at this time only operates its springs DS2, therebyshortcircuiting its upper winding to earth at DT1.

Relay DR also completes at DR2 a circuit for relay DT as follows:battery, DT, conductor 31, normally closed contacts controlled by DTZ,conductor 32, DR2, conductor 33, cable C16, conductor 33, normallyclosed contacts controlled by LS1, conductor 59, start key i springs AS2to earth. At the end of the earth impulses over conductor P01, Fig. 6the circuit of relay DR is opened, and relay DB restores. The initialenergizing earth to relay DS is removed, andk relay DS operatesfullyover both its windings in series and i conductor 4l cableCG,conductor 41, Fig. 1,

wiper 7 of primary distributor switch SW1, first bank contact, conductor42, driving magnet DM4 of secondary distributor switch S/V4t to battery.Magnet DM* is operated and attracts its armature preparatory toAadvancing the switch wipers which, as previously mentioned, are advancedupon the release of the operating magnet. Relay DR also completes at DR3the following circuit `for relay DB, Fig. 3: earth, DB3, conductor 35,DS3., conductor 36, DB3, conductor 43, upper winding of relay DB tobattery. Relay DB is a two-step relay, and at this time only operatesits springs DB, thereby shortcircuiting its lower winding to earth atTM1, Fig. 5, as follows: earth, TM1, conductor 44, cable C11, conductor44, DS, conductor 45, DB4, conductor 46to relay DB. At the end of theearth pulse,'relay DR restores and opens the circuit of magnet DM4,

which releasesiand advances its switch wipers` to their second bankcontacts, relay DR also removes the initial energizing earth for relayDB, and relay DB now locks up over both its windings in series fromearth Aat TM1 over the circuit previously traced. Relay DB in operatingopens at DB2 the impulsing circuit to magnet DM1 of the secondarydistributorf switch SVV4; atDB1 opens the circuit of relay DQ., whichrestores; at DB5 completes 4the following circuit for relay DC, Fig. 3:earth, DB5, conductor 46, relay DC to battery, and at DB3 relay DB opensits own 4initial energizing circuit. VRelay DQJV in releasing opens thepulsing circuit for relay DR.

telay HA, Fig. 4, which was operated by relay SS, at HA1 to HA10inclusive, and relay HB, which was operated at the same time, at HB1 toHB1o inclusive, disconnects the homing earth from the private bank P ofthe secondary switch SW TWhen relay ST operated as a result of theoperation of the automatic start key AS, the

followingcircuit is completed for the ap` SW, Fig. 1, advanced itsprivate wiper P into engagementvwith the second `bank con-y tact as aresult of its magnetDM4 de-enere' gizing, the following circuit wascompleted fer a switch lamp SL1, Fig. 2 in series .with relay LP, Fig.V4: earth, relay LP, Fig.V 4,

ccnductorl, lamp SL1, Fig. 2, conductor 52, cable C9. conductor 52, bankcontact 2 of -z locking circuit: earth, SS2, conductort57,

DB2, lower winding of DE to battery. Relay LSin operating, at thenormally closed cone tacts lcontrolled by armature LS1 opens the circuitof relay DT, which de-energizes.' Relay DS1 which was previouslymaintained by D T does not. release, since contacts LS1 complete analternative holding c` cuit as follows: battery, lower and upperwindings of relay DS in series, DS2, conductor 58, cable C, conductor58, Fig. 4, LS1, conductor 59, automatic start key springs AS2 to earth.Relay DE at springs DE1 prepares a circuit for the primary distributormagnet DMl, Fig. 1. Relay DC, Fig. 3, upon operating prepares a circuitat springs DC3 for twostep relay PT, and at the same contacts removesearth from the homing bank of the sending switch SS, Fig. 3, at springsDC2 prepares a locking circuit for relay PA, at DC*i removes earth fromconductor 60, which extends over cable C19, conductor 60, Fig. 6, andfrom the homing bank P1 of the test switch TS, and at DC4 completes acircuit for the holding coil of the routine time check relay TG2 asfollows: battery, holding coil of time check relay TC?, resistance 1',conductor 6l, cable C, conductor 61, Fig. 4, PU2, conductor 62, cableC1, conductor 62. Fig. 3 to earth at DCt. Moreover at DC1 relay DCremoves `earth from the private bank P of the test control switch TC,Fig. 5 as follows: earth DC1, conductor 63, cable C, conductor 63, Fig.5, and at this same armature completes the following circuit for relayTK, Fig. 5: battery, winding of relay TK, first bank contact in level 3of test control switch TC and its associated wiper, conductor 64, cableC2, conductor 64, Fig. Q, springs 1 of reset key RS, conductor 65, cableC1, conductor 65, Fig. 3 to earth at DCl. A branch of this circuitextends over conductor 66, Fig. 3, cable C17 to conductor 66, Fig. 5,wiper 2 and first contact of the test control switch TC. conductor 67,cable C2T to conductor 67 Fig. 2, faultl lamp 1 to battery. Fault lamp 1upon lighting indicates to tli attendant that the routining operationhas commenced 0n the switch indicated by the previously lighted bay,shelf and switch indiating lamps.

Relay TK at TK1 earths the iirst bank contact with which wiper 4 of testcontrol switch TC is in engagement, and operates magnet DM1 via itsinterrupter springs and causes the switch TC to advance its wipers onestep. At the same time relay TK at TK1 completes the followingr circuitfor relay PU, Fig. 4: earth, TK1, first bank contact of wiper 4 ofswitch TC, conductor 68. cable C20, conductor G8. Fig. 4 and winding ofrelay PU to battery.

Referring now to the time check relays TCl and TG2, Fig. 2, it will beremembered that the holding coil of TC2 was energized by the operationof relay DC. The stepping winding of the time check relay TC2 is at thistime receiving impulses at the iate of 40 per lninute over conductor 69,cable C, conductor 69, Figure 4, PUl, conductor 70, cable C, conductor70, Figure 3, STT conductor 23, cable C16, conductor 23, Figure 4, PMl,conductor 22, cable C23 to pulse conductor PC1, Figure 6. The object ofthese time check relays which are of known construction is to delay thesounding of an alarm in the exchange following a fault indication, sincea switch may be only temporarily busy but in the case of a permanentfault, an alarm will be sounded after a. three-minute interval. Moreoversome of the tests require an appreciable time, say half a minute, tocomplete and it is therefore essential to have some means of delayingthe sounding of the fault alarm. The time check relay TC2 provides thenecessary time interval during the routining operation and the timecheck rela)l TG1 provides a similar interval during the release of theroutine.

Considering now the operation of PU, when this relay operates itdisconnects at springs PU 1 and PU2 the holding and step` ping circuitsto the routine time check relay TC2, Figure 2. lVhen the test controlswitch TC, Figure 5 advances its wipers into engagement with the nextset of bank contacts, it will disconnect the energizing circuit forrelay PU and PU will accordingly release and prepare the time checkcircuits again. At this time earth potential is connected to wipers Qand 3 of the switch TC as previously described and therefore when theswitch advances to the second bank contact the following circuit will becompleted for slow release relay TN Figure 5 battery, relay TN, secondbank contact in level 3 and its associated wiring to earth at DC1 Figure3. As previously stated the stepping magnet DM7 of the test controlswitch TC is connected viav its own interrupter contacts to the wiper oflevel 4 and if this wiper is resting on a bank contact to which earthpotential is connected the switch will automatically advance one stepand connect up a different testing condition. Relay PU, Figure 4. isalso operated in parallel with magnet DM7 over conductor 68 in order todisconnect the time check relay TCF' and allow it to restore. lVith thewipers switch TC in engagement with the second bank contact thefollowing circuitis completed from level 2 for fault lamp FL2, Figure 2lamp FLg, conductor 71, cable C", conductor 71, Figure 5, second bankcontact in level 2 and its associated wiper to earth at DC1, Figure 3.The lighting ofthe lamp FL2, Figure Q, indicates that the switch undertest is busy. either because it is in use or because of a fault.

In order to produce a different operation of the routiner according as aswitch is busy or the corresponding position is unequipped on the shelf.polarized relays PN and PP are provided. Vhn a switch is busy, therelease trunk conductor will be earthed, Assuming that the release trunkconductor connected to the second bank contact of wiper 3 of the.secondary distributor SlV", Figure 4. is earthed, the following circuitis completed l'or llt) relay PP, Figure 5: ea-rth on release trunkconductor connected to the second 'bank contact ofle'vel' 3 of switch'SW1, Figure l', and its associatedl wiper, conductor 72, first bankcontactl in level 4 of switch SlV1 and,l its' associatcdl wiper,conductor 73, cableC, conductor 7 3, Fig. 6, SASBt, MBS, conductor 74e,cable' C, conductor 74, Fig. 4', CBS, conductor '.7'5, cable C24conductor 75, F ig. 5, rto wi er of level 4 of the test switch, Fig. 6',and its first bank' Contact, conductor 76', cable C4, conductor 7 6,Fig. 2", normally closed contacts of private disconnect key PDK,conductor 77, cable C2, conductor 77, F ig.; of', TR1, winding of thevpolarized relay PP, winding of polarized relay PN to' the junctionv ofresistances R1 and R2 the oppositeends of Y stores andlat TR?" removesstepping' earth from the second'i bank Contact in` level 4 of switch: TCand also from the conductor 78, which is connected to first bankAcontact of therlevelI P1 ofthe test switch TS overl conductor 7 Sandvcable G22, This' condition'fnow persists until either the switch undertest becomes"V free or the exchange attendant advances the routiner onto another switchr after l receiving the alarmy and ascertaining thattheswitch islhel'd'wupby` asubscriberl or 1s busy as` theA result of afalultl.

'lif' however the switch position' 1s; un-

equipped, battery potential willl beconnected to tlie release trunkconductor of the unequipped position andf relay PN will1 operate insteadof relay VPP and" at PN1 complete a circuit' for relay TM. Relay ITM'upon operatingrenioves earth at TM1 from conductor 44 and releasesyrelay DB. Relay DB upon releasing rec-onnects relay DQ, to the pulsingconductor 13C-1 whereupon the secondary distributor SVV1 is advanced onestep It may be mentionedl at this.'point-'thatV 1f a key is providedwhich will disconnect DB and alsor thefpulse conductor P61, the'attendant can advance the routiner onto .another switch in the case ofan alarm being `givenv as the result of a fault or a--prolonged busycondition In the arrangement shown however the attendant canV advancethe routiner on to another Vfirst cod'e selector bv operating thecontinuous routine key SRK, Fig. 2, releasingfthe automatic. startV keyAS rand operating the secondary distributor stepping key SDSK,andfvthenreoperating the automatic start key AVS and releasing thecontinuous routine key. p

Assuming now vthatthe fir-strode selector engagediby theseeondarydistributor switch SWi, Fig. 1l, becomes free before the three minutetimel alarm becomes operative,. everything is readyk for the' start ofthey routining operation.

Vhen' the switch' becomes free, earthisfrexy necting earth'to' thedriving magnet DMS over the following' circuit: earth, TRE', Fig.y 5,'FN-1, TKfl, conductor 'T8-,cable G22, conductor 785, Fig. 6,-'firstbankContact of level P1 and its associated wiper,'interrupter springsv andmagnet DMs to'battery.-v Magnet DM8 upon operating' advancesitsfassociated wipersinto engagement with the second set of bankcntactsfin whichl positionA the negative and' positive conductors ofthefirst-code'fselect'or are tested for continuity, contact witheachother, Y

or neighbouring conductors? and contact with e'arthf4 or Ybatterypotential; The test control switch TG will advancei its Vwipers* from'Vsecf ond toithird cont-actsin which' position ift in# dicates the testbeing, performed by lighting ings of relays' TP Vand TA- inA series toearth.

Y Itshould be'eX-plainedthatrelays and TP are low resistance'relays offor instance .1 ohm' each, andf'consequently itv isldesirable topi-Ovidesome safeguard in case direct-battery potential should be connectedythrough these relays.- vThis is taken Careof-r by making relay TDmarginal so that-itwillon-ly )operate over its 2 yohm lower windingwhenfullbatt-ery potential is encountered. Relay TD upon operatingimmediately connects up its highresistance upper winding inseriesf'wit'h rits lower windmgthus reducmgthe current and preventingthe continual blowing .of fuses when Athis condition is encountered.

A The positive line conductor islextended to low resistance relaysTQrand TB and guard relay TJ asffollows t' positive; speaking`conductor, second* bank Contact and" wiper in level 2 offaswitch Sl/V.firstbank contactand wiper in level 3.of switch SW1, conductor 83, cableC6,jconductor 83,/Fig. 6, SAfSB-MB' wiper of lever 3`of switch 'ISfa'ndV its.,v second bank Contact, conductor 84, cable @4,2 con- Gliductor 84, Fig. 2, spring 2 of the positive test key PTK, conductor 85,cable C2, conductor 85, Fig. 5, TG3, Lipper low resistance winding ofrelay TJ, TJ 2, windings of relays TQ and TB in series to battery.Relays TQ and TB are similar to relays TP and TA and relay TJ performsthe same function as relay TD.

In the first code selector the positive and negative speaking conductorsterminate in a battery feed relay. the positive conductor beingconnected through one winding to earth, and the negative conductorthrough the other winding to battery, hence if the line conductors arecontinuous, relays TA and TB will operate. Relays TP and TQy are1narginal, and do not normally operate at this time. The operation ofrelays TA and TB completes the following circuit for slow-to-pulluprelay TO earth, TBl, TQl. TJl, TA1, TPl, TD1, relay TO to battery. RelayTO upon operating completes a circuit over the third bank contact inlevel l of switch TC and its associated wiper for the driving magnetDMT, which advances the test control switch to the fourth set of bankcontacts. At this time fault lamp FL3 is glowing, indicating that theloop test is being applied, and if the test is satisfactory, this lampwill be extinguished when the test control switch advances.

If either of the speaking conductors is disconnected, either relay TA orrelay TB will not operate, andthe switch will not be advanced. If thenegative conductor is in contact with another negative speakingconductor there will be an increased flow of current through the relaysTA and TP, and under this condition relay TP also will operate and openthe circuit for advancing the switch. If the negative speaking conductoris in contact with a positive speaking conductor. the bat` tery feedrelay in the first code switch will be operated over one of itswindings, and the release trunk conductor will be earthed by theassociated guard relay, and this fault will show up as a busy condition.Should there be a very low resistance earth on the positive line or adirect battery connection on the negative line, then either marginalrelay TJ or relay TD will operate, and open up the circuit for advancingthe test control switch. In the event of any one of these faultsoccurring. the test control switch will not be advanced. and the looptest fault lamp T3, Fig. 2 will be glowing, and when the time checkrelay operates, the attendant will know that the loop test is faulty.

In place of the marginal arrangement with relays TA and TP, twopolarized relays could be connected in series across the neutral pointsof a lheatstone bridge arrangement, two arms of which each include awinding of the battery feed relay in the first code switch, while theother two arms comprise suitable balancing resistances. In this case afault on the negative line would operate one polarized relay, and afault on thc positive line would operate the other polarized relay, andin this arrangement the attendant would know straight away which of thetwo conductors was making contact.

lVith the test control switch in fourth position, relays TA, TP and thelower winding of relay TD will be connected to the negative speakingconductor, and relays TB, TQ and the upper winding of relay TJ will beconnected to the positive conductor, and the line and release relays ofthe first code switch will be operated and earth will be applied to therelease trunk conductor. Moreover the following circuit is completed forthe private guard lamp FL'1 battery, private guard lamp 4, conductor 86,cable C27, conductor 86, Fig.

5, conductor 86, fourth bank contact and s wiper of level 2 of switch TCto earth at BCl, Fig. If the operation of the battery feed and `guardingrelays takes place correctly in the first code selector, the earth onthe release trunk conductor will bring about the operation of relay TC,Fig. 4, as follows: battery. relay TC, conductor 87, cable C20,conductor 87, Fig. 5, TN 2, conductor 88, cable C2, conductor 88, Fig.2, normally closed contacts of private disconnect key PDK, conductor 89,cable C, conductor 89, Fig. 6, second contact and wiper of level 4 ofswitch T S to the release trunk conductor of the first code selector.Relay TC upon operating at its armature 3 advances the control switch TCone step by completing the following circuit: earth, TG3, conductor 90,cable C20, conductor 90, Fig. fourth bank contact and wiper in level 4of Aswitch TC to relay PU and also to the driving magnet DMT. The switchTC is thus advanced to the fifth bank contact, and relay PU again setsthe time check relay TG2. Should the guarding earth not be returned overthe release trunk conductor of l?" the first code switch, the testcontrol switch TC would not be advanced, and glowing of the lamp FL4when the time check alarm became operative would indicate the nature ofthe fault.

With the test control switch in position 5, conditions are establishedto enable the routiner to test the correct operation of the switchingrelay associated with the A digit switch selector in the switch undertest. In British Patent No. 264,557 this relay is designated by K and aconnection is made from one side of this relay to a terminal to whichwiper 4 of the secondary distributor switch Sl' "4 has access. When thefirst code selector is taken into use, its line and release relaysoperate and a circuit is completed for setting in operation itsassociated A digit switch selector. When this switch finds an idle Adigit switch, relay K operates and connects up the switch seized. Inorder to test the proper operation of relay K, it is necessary toascertain' that earth potential is connected to conductor KR,

Fig. 1. With switch TC in 5th position, lamp FL5 is lighted over thefollowing cir euit:'battery, lamp F L5, conductor 91, cable C27,conductor 91, 5th bank contact and wiper ot level 2 of switch TC toearth at DC1Fig. 3. The .glowing of this lamp indicates that the K relaytest is in progress.

Assuming earth is duly connected to connected to conductor KR, Fig. 1,it will be eX- tended over bank contact and wiper in level 4 of SWU,contact 1 and wiper in level 5 of switch SW 1, cable C6, conductor 91,Fig.- 6, SAS, SBS, M154, wiper and bank Contact 2 in level 5 et switchTS, conductor '92, cable C21, conductor 92, Fig. 4, TC, conductor 93,cable C20, conductor 93, Fig. 5, winding ot' relay TE to battery. RelayTE operates and completes a circuit for relay TF at armature 1. Relay TFoperates and at TF 2 earths the 5th bank contact in level 401 switch TCthereby advancing the switch to the 6th position. The lamp FL5 remainsalight rhowever due to the 5th and 6th contacts being ,multipled RelayTF also at TF1 prepares a circuit for relay TH.

The circuits remain in this condition until the time pulse relays in theA digit switch Operate and bring about the release of the A digitswitch. l/Vhen this happens, earth potential is removed from the KRconductor and relay TE, Fig. 5, releases, thereby coni'-Y leting thefollowing circuit for relay TH; earth, TEl, TF1, relay TH to battery.Relay TH upon operating completes a circuit :tor relay TG at THl and atTHZ prepares a circuit for advancing the testswitch TS and at TH3 earthsthe 6th contact in the bank et level 4 of switch TC, thus operating thedriving magnet Dil/i7 to advance the switch to 7th position. Thisdisconnects the fault lamp FL5 and connects up the lamp FL6 whichindicates that the first code selector is being held on a loop with theA digit switch released. Lamp FL6 is lighted over conductor 94, cableC27, the 7th Contact in the bank of level 2 of switch TC to earth. lVhenrelay TE releases, it opens the circuit of relay TF which also releasesand the circuit is now completed for magnet DM8 of the test switch TS asfollows: earth, TEl, TF1, TH2, (TH being slow to release holds up foran` instant) conductor 95, cable C22, conductor 95, Fig. 6 to the magnetDM8 of switch TS. Magnet DMS does not advance the wipers until itscircuit is opened at TH2 by the falling away of slow relay TH,whereuponV the wipers of the switch TS arev advanced into engagementwith the 3rd set ot bank contacts. .Vith relay TG in operated positionandTH deenergized, earth is connected to the 7 th contact in level 4 ofthe testcontrol switch TC as follows: earth, THS, TGS, 7th bank contact,

operated it opened the loopcircuit extendingxu to the first codeselector fat contacts TGzyaxrd TG3 and this operation caused fthe rlineand release relays of the .first code Vselector to fall Then the first`code selector releases earth is normally-removed from the releaseytrnnk conductor of the switch and thisr leaves the switch free tobeseized by anyhnnting line switch Y In order to prevent thisoccurring,relay TN is operatedto place a guarding learth on the release trunkconductor of the-j first code selector under test. Relay TN is operatedfrom battery, relay TN, bank contacts 7 and 8 of level 3 of switch TCand the associated wiper to earth. Relay TN in operating earths theprivate lead P, Figi extending to the release trunk conductorfof thefirst lcode selector under .test fromearth. TN'2, conductor 88, cableC2, and thence over the circuit previously traced, thus busying th-e rstcode selector to any hunting line switch during the time the tirst codeselector is releasing and until it is again operated by the rontiner.When relay TG releases, earth is connected toy the 8th bank contact inlevel 4 of switch TC and-the switch is advanced to 9th position. VInthis position lamp FL7 is extinguished and lamp FL8 is lighted overLconductor 102, cable C27, conductor 102, 9th bank contact -in level 2of switch TC -to earth at D01, Fig. 3.

Upon the release of relay TG'and the movement of the test switch tothird position, the following loop isV closed across ythe lin-econductors of the rst code selector under test: negative speakingconductor, secondi'.

bank contact in level y1 of secondary distributor STW, first bankcontact and level 2 of primary distributor SVVl, conductor 80, cable C,conductor 80, Fig. 6, SA, SB, MB1, wiper and third bank Contact` inlevel 2 of. switch TS, rconductor 98, cable (321 conductor 98,PR3,..conclt1ctor 99, cable C16, conductor 99, Fig, 3, PE2 and PE1inlparallel, conductor 100,;cable C17, conductor 100, Fig. Ali, cableC1, TG, conductor 101, cable C22, corr ductor 101 Fig. 6, third bankContact in level 3 of test switch TS and associated wiper, to thepositive speaking conductor over vthe -previously't-raced circuit. Theline relay rofthe Y the switching relay conductor KR, Fig. 1 from thefirst code selector. Fault lamp FL* indicates that a test is being madeof the forced release from a seized register controller.

In order to gain access to a register controller, it is necessary totransmit a series of impulses to opera-te the A digit switch which willthen take into use an idle register controller. With the test controlswitch in po* sition 9, relay PS, Fig. 3, is operated as follows:battery, relay PS, conductor 96, cable C, conductor 96, Fig. 5, bankcontact 9 in level 3 of switch TC to earth at DS1, Fig. 3. Relay PS uponoperating at PS1 completes a circuit for PA which upon operating locksup at PA2 to earth at DC2. Relay PA also completes a circuit at PA1 forthe vibrator V which is employed for transmitting impulses at springs V2in known manner, and at PA3 completes a circuit for advancing thecontrol switch TC over the conductor 9T, able C", conductor 97, Fig. 9thbank contact in Vlevel 4 of switch TC and its associated wiper to magnetDMT. Magnet DMT operates and advances the switch wiper to the 10th setof bank contacts. In this position lamp FLg is disconnected and lamp FLlighted over conductor 103; this indicates that the first code selectoris being held waiting for the forced release to become effective.

Upon the operation of the vibrator V impulses at the rate of l() persecond are produced at Contact V2 and are transmitted to relay PE asfollows: battery, relay PE, PCi, PDI, V2 to earth at PA1. Relay PEaccordingly impulses at the rate of 10 per second and at springs PE1transmits impulses to the sending switch magnet DM5. Impulses are alsotransmitted to the line relay of the first code selector under test bythe operation of springs PE2. lVhen the sending switch SS advances fromnormal to second position, a circuit is completed for slow relay PP, andPB upon operating, at PB1 removes a shortcircuit from the impulsesprings PE2. at PE2 prepares a circuit for relay PT, at PB3 prepares acircuit for relay PD, and at PB prepares a circuit for relay PC.

The first operation of impulse springs 2 of relay PE is ineffective,since they are shortcircuited by springs 1 of relay PB. The seeondinterruption of springs 2 of relay PE effects the transmission of animpulse to the line relay of the first code selector over conductors 99and 100 and the previously traced circuit to the windings of the firstcode selector line relay. A second impulse is transmitted in a similarmanner and the seuding switch is advanced from third position to fourth.In this position of the sending switch SS the following circuit iscompleted for stop relay PC: earth, wiper and 4th bank contact in level2 of switch SS, PB", winding of stop relay PC to battery. Relay PC uponenergizing opens the circuit of PE at PC1 and thus prevents furtherimpulses from the vibrator contacts V2 from becoming etliective. RelayPC also at PC2 opens the locking circuit for relay PA which releases andstops the vibrator. The lirst code selector line relay repeats these twoimpulses to the A d'fit switch which har-f. been associated therewithand this switch steps up to the second level and selects an idleregister controller. lllheu the first code selector is connected to anidle A digit switch, earth is connected to conductor KR, Fig. 1, andthis potential operates relay TE as before and relay TE operates relayTF. Relay TF upon operating pre-` pares a circuit for relay TH aspreviously described. Since no further impulses are transmitted to theregister controller its own forced release control will become operativein due course and earth will be removed from the conductor KR, Fig. 1,and relay TE will release. Relay TE upon releasing operates relay TH andreleases relay TF. lVith relay TH operated, earth is connected to the10th contact in bank l of the test control switch TC and the drivingmagnet DM7 advances the wipers of this switch to the 11th position. Inthis position lamp FL9 is extinguished and lamp F L10 lighted overconductor 10st. The lighting of lamp FL10 indicates that the forcedrelease from the register controller has taken place satisfactorily andthat the first code selector is held in a loop circuit. lVhen relay TFreleases, it completes a circuit for the magnet DMS of the test switchTS, whereupon magnet DHS energizes but does not advance the wipers untilTH releases. Relay TH also opens the circuit of relay TG which removesthe loop circuit which is holding the lii'st code selector. By therelease of magnet DMS the wipers of the test switch TS are advanced fromthe third to the fourth set of bank contacts. lVith the switch TS infourth position, circuits are prepared for connecting a resistance inseries with the loop extending to the first codel selector in order thatmarginal operation of the relays of that switch may be tested.Furthermore in this position meter lead M, Fig. 1, is extended to relayTY in order to permit the metering operation to be subsequently checked.

lVhen relay TH released it completed a circuit over TH2, TG. 11th bankcontact in level 4 of switch TC to the 'iagnet DM", which accordinglyadvances the wipers from the 11th position to the 12in position. ln thisposition lamp FLN will be extinguished and lamp FL11 lighted overconductor 105. Then relay TG releases, another circuit is completed foradvancing the switch TC over bank contact 12 in level 4 of switch TC tothe magnet DM7 and the wipers are advanced from the 12th position to the13th position and lamp FL11 is extinguished and lamp FL12v lighted overconductor 106.i When wiper?) of switch TC is in `engagement with the11th bank Contact, it completes a circuit for relay TN, .which uponoperating,vfeeds guarding earth back to the conductor P, Fig. 1, aspreviously described.A yRelay TN remains operated when the switchadvances from its 11th to 12th position inA order to maintain therelease trunk guarded during this interval. The lighting of lamp F L12dicates that the iinpulsing test is being applied to the iirst codeselector.V When/relay TG released it again completed a loopcircuit tothe iirst code selector, resistance 115, Fig. 3 being now included inserise with the loop as follows: conductor 100, Fig.'3,lcable C,conductor 10.0, TGS, conductor 116, cable C, conductor 116, Fig. '3,series resistance 115, PT, conductor 117, cable C19, conductor 117, Fig.v 6, 1th bank contact in level 3 of test switch TS and associatedwiper, MBZ., SBE, SAconductor 83, Fig. 1, cable C6, Wiper and bankcontact in level 3 of switchSll, wiper and .banki contact in level 3 ofswitch SWi to the positive speaking conductor. Y The other sideof theloop extends tothe negative speaking conductor over the same circuit aspreviously described. Due to thisloop .the line relay .in the iirst codeselector is re-operated through the high resistance 115.

In order to check that the line relay responds properly' to impulsesthrough this resistance, the `digits 666 are transmitted to the lirstcode selector by which they are rrepeated to a register controller. Inthe 13th position of switch TC, relay PrS, Fig. 3 is operated overconductor 96. Relay PS will operate PA again and relay PA kwill startkup the vibratorlV andV relay PE will startV impuising over the loop aspreviously described. The sending switch SS 1n passing rom contacts elto 11 will send siX impulses before relay PD is operated. IRelay PAinoperating places earth on the V13th bank contact in level 4 of switchTC .and driving magnet DM7 advancesA the wipers of the' switch to the14th position. In 'this position lamp F1112 isextinguished and lampF1113 is lighted overconductor 108, thusrindicating that the registercontroller is in a. condition to respond to digits repeated from thefirst code selector. Relay TU is :operated when thetest control switchis standingin the 111th position in orderl to place a shunt resistanceacross the loop circuit orthe lirst code selecto relay TV whichoperates, and vTUL prepares 'the shunt resistance circuit-whichy will betraced later. Relay PD is operated from battery, windingv of relay PD,Fig. 3,`PB3,

bank contact 11 in level`2 .of sending switch SSandassociated vwiper toearth. Relay PD at PD.1 disconnects relay PE whichy releases in order to.prevent further impulses being sent to the first `code selector yundertest, and atPD2 completes a circuit for two-step relay PT `from earth,FB2, PD2,P'1`2, upper Winding for PT to battery. Relay .PT at this timeonlycloses contacts PT3 short-circuiting its lower winding to earth atDCS.- `l/Vhen the sending switch SSmoves from position 10 to positionI11-tl1e circuit ofslow `releaselrelay PB is yopened and relay PB`releases, and at PE2 removes the initial energizing earth `from relaywhich operates ullyfrom earth, PC, PTS, windingsV of relay PT in seriesto battery, atrelay PT.2 opens yits initial energizing circuit and atPT4 removes the series resistance. 115 from the loop to the negative andpositive kspeaking conductors and yat PT,l

aok

closestheshunt 'resistance circuit across the speaking conductors `asfollows.: negative speaking conductor, second bank contact and wiperyinr level i1' of secondary distributor switch' Sl/V4, Fig. 1, `firstbank contact :and

wipersin level k2 of Aprimary distributor switch and PBl 'inparallehconductor 100, cable C17,

conduct-or 100, Fig.`5, TG6,-conductor `116,

cable Clconductor 116, Fig.V 3, PTconfk ductor 117, cable C19, conductor117, Fig.f6,

11thV bankcontact and wiper in level 3 of Vtest switch TS, MBZ, S135-,SAS, conductoryk '83, positive speaking conductor. The shunt resistanceis placed across the loopjfromiconductor 100, resistance 118, PT?,conductorl19, cable Qlconductor 119, Fig. 5, TU?, conductor 120,cableC2?, conductor 120, Fig. 4, to'PB. PBupon releasing, at PBZ opens thecircuit of relay PD which releases, and at PBI short-circuits theimpulsing springsof relay PE inorder to render these ineiective. RelayPD inreleasing at PDlconipletesthe circuit to relay P E which will start`impuls-jing over the loop as Previously described. Sending switch'SS,Fig". 3, willlnow be `moved from position 14 toposition 20 and will sendout siX- impulses before relay PD is again operated'in themanner'previous'ly described. Relay PD in operating disconnects relay PE'which releasesfand prevents'further impulses being delivered to the`first code selector. Sending yswitch SS in passing from position 2O topositionQl ,opens the circuit otrelay PB which releases and Yopens acircuit for relay PDgwhich-falso releases after :an interval..

PD in releasingy closes` a circuit to relay PE which will startnimpulsing l'over loop as pre-` viously described; Sending switch SSwillnow inove from position 21it0 position2`5 and siX further impulses willbe `delivered to the loop circuit of the first code selector under testbefore relay PC is operated as before described. Relay PC at PC1disconnects rela PE to terminate impulse sending and at Cz opens thecircuit of relay PA which releases and disconnects vibrator V. Senderswitch SS in passing from position 24 to position 25 opens the circuitof relay PB which releases and opens the circuit of relay PC whichreleases also.

In this manner, three series of six impulses have been delivered to thefirst code selector, the'first or A digit being received lby the A digitswitch and the second and third or B and C digits by the registercontroller which is selected from the 6th level of the A digit switch.The register controller is now caused to send out series of impulseswhich will route the connection from the first code selector under testthrough suitable exchange selectors to thevacant local selector levelwhich is connected back to the routiner. The register controller and Adigit switch will then be disconnected from the switch train leaving thewipers of the first code selector switch connected through to terminals14 and 15 and thence to relay TT. This circuit ext-ends from battery,upper winding of relay TT, Fig. 6, normally closed contacts controlledby armature TL2, conductor 11, cable C4, conductor 11, Fig. 2, junctiontest key springs JT, resistance r, junction test key springs J T2,conductor 12, cable C1, conductor 13, ST2, negative terminal 14, backbridge in first code selector, positive terminal 15, ST3, conductor 18,cable C1, conductor 18, junction test key springs JTl, resistance r2,resistance r3, cable C, conductor 18, Fig. 6, normally closed contactscontrolled by armature TL1, lower winding of relay TT, conductor 19,cable C22, conductor 19, Fig. 5, armature TG5 to earth. This circuit isof course only completed if the line relay of the first code selectorhas correctly repeated the digits 666 sent under varying lineconditions. Relay TT in operating at TT1 completes the circuit: earth,conductor 121, cable C, conductor 121, Fig. 5, 111th bank contact inlevel of the test control switch, magnet DM7 to battery whereupon thewipers are advanced to the 15th position. In this position lamp FL14 islighted over conductor 108 to indicate that the holding feature of thefirst code selector is under test. The control switch TC in passing fromcontacts 14 to position 15 opens the circuit of relay TU which releasesand opens the circuit of the relay DB. The test control switch TC inposition 15 completes a circuit for relay TG;

attery, winding of TG, conductor 122, 15th bank contact in level 3 ofthe switch TC and associated wiper to earth at DC1. Relay TG inoperating, at TG5 removes earth from lower winding of relay TT andreplaces it by battery through resistance 123, and at TGe opens thecircuit to the first code selector under test. This condition isequivalent to the holding condition on a call to an operators positionwhen the calling subscriber opens the calling loop by hanging up hisreceiver or to the silent period during busy flash. This conditionpersists until slow relay TV releases and during this time earth shouldbe maintained on the release trunk conductor in order to guard thatswitch from intrusion. When relay TV falls away, earth is supplied tobenk contact 15 of the test control switch TC over conductor 124, TV2,conductor 90, cable C2", conductor 9() and TG3. Driving magnet DM1 ofthe test control switch operates and advances the wipers to the 16thposition. Should earth for an reason be removed from the release trunconductor during this period, relay TC would release and at TC3 removestepping earth thereby preventing the advance ot the switch TC. The testcontrol switch TC in passing from position 15 to 16 opens the circuit ofrelay TG which releases and at TG1 closes the circuit of relay TU;battery, winding of relay TU, conductor 125, TG1, conductor 126, 16thbank contact and wiper in level 3 of the test control switch T C toearth at DCI. Relay TU operates and at TU1 completes a circuit for relayTV which operates also. Relay TV in operating at TV3 connects earth tocontact 16 in level 4 of the test control switch TC and the drivingmagnet DM7 advances the wipers of the test switch from the 16th to the17th position. In moving from position 16 to position 17 the switch TCopens the circuit of the relay TU which releases and opens the circuitof relay TV. The switch TC also extinguishes fault lamp FL14 and lightsfault lamp FL1r over conductor 109 in order to indicate that the test ofthe metering operation is being conducted. Relay TV in releasing closesa circuit for relay TL; battery, winding of relay TL, Fig. 6, conductor127, cable C22, conductor 127, Fig. 5, TV1, a conductor 12S, bank contact 17 and wiper of level 3 of the switch TC to earth at DCR Relay TLin operating at TL1 and TL2 reverses the connection of the windings ofrelay TT to the back bridge at the first code selector. This reversesthe direction of the current flowing through the polarized relay at thefirstcode selector whereupon this relay should operate to initiatemetering. This will result in the connection of earth to lead M, Fig. 1,whence it is extended over bank contact 2 and level 2 of secondarydistributor SV, first bank contact and wiper in level 6 of the primarydistributor SVVl, conductor 129, cable C", conductor 129, Fig. 6, SA?,SB?, MB", conductor 130, wiper and 4th bank contact in level 6 of thetest switch TS, Fig. 6, conductor 131, cable C, conductor 131, Fig. 2,normally closed contact of the meter fail key MFK,

Fig. 2, conductor 132, cable C4, conductor 132, Fig. 6, relay TYv tobattery. The operation of relay TY at TY1 earths the 17th bank contactin level 4 of the test ycontrol switch by way of conductor 133, cableC22, conductor 133, Fig. 5, 17th bank contact in Y level 4 of the testswitch TC, Fig. 5, whereupon the driving magnetDM7 advances the of relayPR, Fig. 4, conductor 134, cable C20, A

conduct-or 134, Fig. 5, 18thbank contact and wiper in level 3 of thetest control switch TC to earth at LDCl. Relay PR in operating, at

'PR1 removes earth from contacts 22 to 25 in level P1 of the releasetiming switch RT, Fig.

, 4, in order to permit the switch to stay oit normal, at PR3 opens thecallingloopv to the hrst code selector in order to start the release ofthe latter, and at PR2 closes a circuit from the pulse conductor PC2,cable 23, conductor 135, Fig. 4, PR2, TC2, CC2, lower winding oftwo-step relay CC to battery. Upon the iirst earth pulse, the lowerwinding of relay CC energizes and at this time only closes co-ntactsCCl, thereby short-circuiting its upper winding by earth, RC1, F ig.y 4,RF1, CCl. At the end of the iirst earth pulse from the pulse conductor,the initial` energizing earth is removed from the lower winding ofVrelay CC. Relay CCk now operates ltully. over both its windingsin-series from earth., RC1, RF, CCl,

windingsof relay CC in series to bat;eryand` at CC2 switches the pulseconductor PC2 toV the driving magnet DM of the release timing switch RT.Thus earth paises at the krate of 2O per second are delivered to thedriving lease trunkk conductor after the maximum magnet DM6 whichadvances the Wipers of he release timing switch RT over their bankcontacts at the rate of 2O steps per second.

Y iVhen the irst code selector releases owing to the opening of the loopearth is'removed from the release trunk conductor and relay TC releasesand places 'earth on thewviper of level 2 of the releaseftiming switchYby way oi PRl, TCl, and conductor-136, and at TC2 disconnects the 2Oper second pulse conductor PC2 fromthe driving magnet DMG. Should therelease take place within the ale lowable limits, the release timingswitch will be standing lon one of contacts 8 to 13 and relay RC thenoperates ffrombattery, winding of relay RC, conductor 13'?, contacts 8to 13 of switch RT, wiper of release timing switch to earth. Relay RCin'ope'rating yat RCl opens the circuit of relay CC which releases, atRC2 places'an earth on the 18th bank contact in Ylevel 40h-the testcontrol switch TC by way of conductor 133, RF2, conductor'139, cableC2", andy conductor 139", Fig. 5, so that the driving magnet @M7advances the wipers in the'usual manner tot-he 19th position. Earthisnow kplaced on the 19th bank contact in .level 4 ot the test controlswitch yover RC2, conductor 140, cable C20, and conductor 140, Fig. 5,whereupon rthe driving `magnet Dls/17 advances the wipers of the'switchto the 20th position. In this position the fault lamp FL is lightedoverconductor-112 to indicate that the release tiniing test hasbeensuccessful. The test con? trol switch in passing from position 19 toposition 20 opens the circuit of relayVPR which releases and at PR1removes 'earth from the wiper 2 of the release timing switch RT therebyopening the circuitv of relay RC and also places earth on contacts 2 to25 in 'level -P of the release timing switch RT thereby operatingdriving magnet Dil through its own interrupter springsto return therelease timing switch to its home position. Relay RC in releasing placesearth on the 20th bank contact of the test control switch over RC2,conductor 141, cable C2o and conductor 141, F ig. 5, and the drivingmagnet DM7 advances the switch tothe-21st position. f f

Should the earth be removed fromthe release trunk conductor before theminimum permissible interval has elapsed, the release timing switch RTwill be standing on one of contacts 2 to 7 and upon the release ot relayTC relay RF will be operated from earth on wiper 2. In thesecircumstances no earth will be placed on the 13th bank contact in level4 of test control switch and so the switch does not step. ln thisposition faultglamp F111` is'iighted over conductor 110, to indicatethatlfast release has taken place and an alarm will be given after theusualthree minutes delay.

Should theearth be removed from the repermissible interval has elapsedthe release timing switch RT'w'ill be standing on one of contacts 14 to25 and relay RF will then be operated over its lower winding. Underthese conditions an earth is placed on the 18th bankfco'ntactin level 4of thetest control switch TC by way of wiper 2 of the release timingswitch, contacts 14`to 25, conductor 142, RF 2, andk conductor 139, andthe driving magnet DM7 accordingly advances thewipers of the testcontrol switch to the 19th position. In this position fault lamp FL16 isextinguished and lamp FL17 lis lighted over conductor 111 and toindicate that slow release has taken place and the alarm willYconnecting upfof the next ylirst code selector since the previous testhas now been completed. Relay TM in operating at TM1 opens the circuitof relay DB which releases, thereupon at DB5 opening the circuit ofrelay DC which releases also. Relay DC in releasing at DC2 places anearth on bank contacts 2 to 25 in level P1 of the sender switch SS so asto effect the restoration of the sender switch SS to its home position,at DC'1 removes earth from the holding coil of the routine time checkrelay TC2, Fig. 2, thereby causing it to release in preparation forroutining the next first code selector, at DC5 places an earth by way ofconductor GO, and cable C19 on conmets e t0 4, e i0 s, 10 t@ 1Q, il to1e, is to e0, 22 to 25 in level P1 of the test switch TS, Fig. G so thatdriving magnet DMS advances the test switch TS to its next homeposition. Relay DC moreover at DC1 removes earth from wipers 2 and 3 ofthe test control switch TC and at its resting contact, places an earthover conductor 63 and cable C17 on contacts 2 to 25 in level P of testcontrol switch TC whence it is extended over the wiper and interruptersprings to the winding of magnet DM7 so that the test control switch TCis rotated to the home position in known manner. Relay DB in releasingconnects the 40 per minute pulse conductor PC1 to the twostep relay DQ.,Fig. 3, which operates in the manner previously described. Pulseconductor PC2 is thus connected to relay DR, Fig. 3, which pulses at therate of 40 per minute.

Upon the first operation of relay DR earth is connected to the drivingmagnet DM4 by the secondary distributor SW1 in order to step the latterto make connection with the next first code selector switch. The circuitextends from battery, DM1, conductor 42, 1st bank contact and wiper inlevel 7 of the primary distributor SV1, Fig. 1, conductor 41, cable C",conductor 4:1, Fig. 6, SA2, conductor 40, SB2, MB5, conductor 38, cableC2, CR1, conductor 37, cable C18, conductor 37, Fig. 3, DB2, conductor36, DS, conductor 35, DR3 to earth, and magnet DM1 is operatedpreparatory to advancing the wipers. A circuit is also completed for theupper winding of two-step relay DB; battery, upper winding of relay DB,DB3, conductor 36, DS3, conductor 35, DR3 to earth, but at this timerelay DB only operates its contacts DB4 thereby short-circuiting itslower winding by earth from TM1, Fig. At the end of the first relay DRreleases, thereby removing earth from the driving magnet DM'1 of theSecondary distributor switch SlV whereupon the wipers of the switch areadvanced to the next set of contacts and make connection with the nextfirst code selector switch to be tested. Relay DR also removes the earthfrom the junction of the windings of relay DB so that DB now operatesover both its windings in series from earth at TNP. Relay DB inoperating, at DB1 brings down two-step relay DG so that no more pulsesare delivered to relay DR, and at DB5 completes a circuit for relay DCwhich operates, and initiates the test cycle on the first code selectorto which the secondary distributor is now connected. The secondarydistributor, upon stepping will light lamp 2 of thc switch lamps SL,Fig. 2, over conductor 143, thus indicating the switch in the shelt' towhich the connection has been made. Upon the completion of a successfulroutine test on this switch, relay TM will again be operated and willrelease relay DB as before described.

In this manner a complete shelf of 2() first code selector switches isroutiued and the secondary distributor switch Sli, Fig. 1 is thenstepped from position 21 to position 22. In this position the circuit ofrelay LP through the switch indicating lamps SL, Fig. i2, and bankcontacts 2 to 21 of the switch SlV* opened and relay LP releases.thereupon opening the circuit of relay LS which releases also. Relay LSin releasing, at LS1 opens the locking circuit of two-step relay DSwhich releases. Relay DB will also be released by TM operating after thecompletion of' the testof the 20th switch in that shell' and closes acircuit for DQ and hence for relay DR as before described. Owing to therelease of relay DS however, a circuit is now completed for advancinffthe first primary distributor to connect with the second secondarydistributor. The initial operation of relay DR completes a circuit forthe driving magnet DM1 of the primary distributor SlV1 from battery,winding oi magnet DM1, conductor 14.11, cable C, conductor 14:1, Fig. 6,DX1, conductor 145, cable C2, conductor 145, Fig. 5, CH3, conductor 146,cable C18, conductor 146, F 3, DB1, ST, conductor 147, cable C18,conductor 117, Fig. 5, CR2, conductor 148, cable C18, conductor 11S,Fig. 3, DS3, conductor 35, DR3 to earth. Relay DR also at DB1 closes acircuit for two-step relay DS from earth, conductor 1419, ST5, DS1,lower winding of relay DS to battery, and at DB2 completes a circuit forrelay DT, Fig. 3, which operates and locks up as previously explained.Relay DS at this time only operates its contac'ts DS2, therebyshort-circuiting its upper winding by earth from DT 1. At the end of thefirst pulse, relay DR releases thereby removing earth from the drivingmagnet- DM1 of the primary distributor Sli'Y1 so that the wipers of theswitch are moved to the second set of contacts thereby enabling theroutiner to gain access to the next secondary distributor. The releaseof relay DR- also removes the initial energizing earth from the twosteprelay DS which now operates over both its windings in series from earth,DT1, DS2, windings of DS in series to battery. The next operation ofrelay DR over pulse conductor PC1 at DR3 energizes the upper winding oftwo-step relay DB as previously explained.

Relay DR also at DR?` completes a circuit for the driving magnet of thenext secondary distributor to which'the Vprimary distributor SW1 is nowconnected extending fromearth, DR3, DB2, conductor 37. cable C18,conductor 37, Fig. 5. SR1, conductor 33', cable C26 conductor38, Fig. 6,MBS, conduct-or 39. SR2, conductor 46, Sir/'12, conductor 41, Acable i2,conductor 41, Fig. 1, wiper and second bank contact in level 7 of theprimary distributor SN1 and driving Vmagnet of secondary'distributor(not shown) to battery. The driving magnet of this switch nowy energizespreparatory to stepping the wipers. Relay DR releases upon thetermination of thezimpulse and removes the initial energizing earth fromrelay DB which operates over both windings in series as previouslyexplained. Moreover at DB3 the earth for the driving Vmagnet of .thesecondary distributor is re- Fig. 1, second bank contact inlevel 8 ofthe primary distributor Sll71,conductor49, cable C6, S111, conductor 48,SR1, conductor 47, cable C2G, conductor 47, Fig-5, cable C18, conductor47 Fig. 3, to earth'at ST1. The secondary distributor upon advancing to.the second bank contact closes the circuit for relay LP, Fig. 4gbattery, winding of rrelay LP, conductor 51, lamp SL, Fig. 2, conductor52, cable C2, conductor 52, second bank contact and wiper in level Pofthe secondary distributor, interrupter springs, driving magnet tobattery. Relay LP operates in this circuit and lamp SL11 glows but thedriving magnet does not operate due to the resistance of lamp SL1. RelayLP in operating completes a circuit for relay LS which operates aspreviously described. Y

The routine tests are now applied successively to the switches in theshelf served by the secondary distributor 'with which the routiner isnow connected. At the end of each complete test the secondarydistributor will be stepped in order to connect to the next switch inthe shelfv as above described. The

i; primary.distributor will be stepped upon the completion of asuccessful routine test of any particular shelf of first codeselectorsin the manner previously explained 'until all the first codeselectors to which the primary dis-y tributor N1 has access have beenroutined.

In order that the routiner may connect with first code selectorswitch-es to which the second primary distributorSl71 has access, the thbank contacts of levels 2 to 8 of the vfirst primary distributor Sl-T1are .connected through to the wipers of levels 2 to 8 of the secondprimary distributor SW2, so that when the wipers ofthe switch SW1 reachtheir 25th cont-acts the leads to the rountiner are connected through tothe second primary distributor .Svi-l2. Moreover, relay DXris nowoperated from battery, winding ofrelay DX, conductor 158, cable C19,conductor 158, Fig. 3,`SS1, conductor 159, cable C7, conductor 159, Fig.1, 25th bank contact and wiper inlevel P1 of the primary distributor SWto earth, and thereupon switches the pulsing circuit from the drivingmagnet DM1 of the first primary distributor SW1 to the driving magnetDM2 of the second primary distributor SW2. The circuit extends frombattery, Winding of driving magnet DM2, conductor 151, DY1,0DX1,conductor 145, cable C26, conductor 145, Fig. 5, CR3, conductor 146,cable C18, conductor146, Fig. 3, DE1, ST6, Vconductor 147, cable C18,conductor147, Fig. 5, SR2, conductor 148, cable C12, conductor 148,Fig.v 3, DS3, DR3 to earth.

The' first codeselectors to which the second primary distributor SW2 hasacc-ess are routined in the manner previously described and the secondprimary distributor will finally step to the 25th position. In thisposition the leads 'from the routine'r are switched through to the thirdprimaryl distributor and relay. DY is alsoV operated over the circuitbattery,

winding4 of relay DY, conductor 152, cable C1?, conductor 152, Fig. 3,SSB, conductor 153, cableC7`, conductor 153, Fig. 1, 25th bank contactand Wiper of secondary distributor SW2 to earth. The pulsing circuitthus pre'- paredfor the driving magnetr DM3 of the third primarydistributor SW3 is as followed-battery, driving magnet'` DME, conductor154, DY1, DX1, conductor 145", cable C26 to earth at DRS, Fig. 3, overthe circuit previously traced. f

The first code selectors to Which'the primary distributor SVa has accessare routined in the manner previously described and4 in' duey course theprimary. distributor is stepped from position 19 yto position 20. Sinceall the lfirst code selector switches inl the exchange have been tested,it is necessary to give a signal to indicate that the routining isifinished. This is done by relay SP which is y now operated as followsz-battery, winding of relay SP, Fig. 6, conductor 155, cableC, conductor,155, Fig. 3, SS5, c0nductor156,` cable C7, conductor 156, Fig. 1,contact20'i`n level P ofthe third primary distributor SW3 andassociatedwiper to earth. -RelaySP in operating, at SP1 lights theroutine finish .lamp FL20 from battery, lampFL20, conductor 113, SP2 toearth, and at SP2 operates relay PM from battery, lowerk winding ofrelay n the attendant that the routining operation has been completed.

In order to restore the equipment t-o normal, the attendant releases theautomatic start key AS whereupon the circuit for relay ST is opened andit releases and at ST1 opens the circuit for relay SS which releasesalso. Relay SS in releasing closes circuit for relays ZA, ZB, ZG whichrelays operate and close restoring circuits to the magnets DM1, DM2 andD3 of the primary distributors S1171, S1172, S1173. Relay ZA is operatedat this time from battery, winding of relay ZA, conductor 160, cableG11', conductor 160, Fig. 3, SS1, conductor 159 to earth at wiper P1 ofprimary distributor S1171 over the circuit previously traced and mayalso be operated over conductor 160, SSB, conductor 162, cable G1,conductor 162, Fig. 1, contacts 2 to 24 in level P1 of the primarydistributor S1171 and associated wiper to earth. Relay ZB similarly isoperated from battery, winding of relay ZB, conductor 161, cable G19,conductor 161, Fig. 3, SS1, conductor 153 to earth at wiper P1 ofprimary distributor S1172. Relay ZB may also be operated over conductor161, SS1, conductor 163, cable U, conductor 163, Fig. 1, contacts 2 to24 in level P1 of the primary dis tributor S1172, and associated wiperto earth. Relay ZG is operated from battery, winding of relay ZG,conductor 164, cable G19, conductor 164, Fig. 3, SS5, conductor 156 toearth at wiper P1 of the third primary distributor S1173, and may alsooperate over conductor 164, SS, conductor 165, cable G7, conductor 165,Fig. 1, contacts 2 to 19 in level P1 of the third primary distributorS1173 and associated wiper to earth. Relays ZA, ZB, ZG in operating, atZA1, ZB1, ZG1, complete a circuit for relay PL over conductor 166, cableG21, conductor 166, Fig. 4, relay PL to battery, at ZA2, ZB3, ZG3connect holding earth to relay DQ over conductor 167, cable G19,conductor 167, Fig. 3, in order to replace that removed by STB, and atZA2, ZB2, ZG2 complete a' circuit from the 40 per minute pulse conductorPG1, cable G23, conductor 22, Fig. 4, P1111, conductor 168, cable G21,conductor 168, Fig. 6, ZA2, ZB2, and ZG2 in parallel, conductor 169,cable G21, conductor 169, Fig. 4, conductor 70, cable G16. conductor 70,3` DQ1, conductor 24. DB1, conductor 25, lower winding of relay DQ tobattery. Hence pulses at the rate of 40 per minute are delivered torelay DQ. and when this operates fully, to the relay DR which pulses inthe manner previously described. A homing circuit for the primarydistributor S1173 is now completed from battery, winding of magnet DMS,conductor 154, ZG, conductor 17 0, cable G19, conductor 170, Fig. 3, ST,conductor 147, cable G18, conductor 147, Fig. 5, GR2, conductor 148,cable G18, conductor 148, Fig. 3, DS3, conductor DR3 to earth. Pulses ofcurrent are therefore fed to the driving magnet DM3 and the switch S1173is rotated to the home position. 117hen this is reached, the circuit ofrelay ZG is opened and it releases and completes a homing circuit forthe switch S1y 72 as follows battery, winding of magnet D112, conductor151, ZB, ZG1, conductor 170, cable G11 to earth at DR2. 117hen theswitch S1172 reaches normal position, relay ZB de-energizes and thefollowing circuit is then completed for homing the first primarydistributor battery, winding ot magnet DM1, conductor 144, cable G6,conductor 144, Fig. 6, ZA, ZB1, ZG1, conductor 170, cable G19 to earthat. DR2, Fig. 3. Hence the switch S1171 advances to its normal positionwhereupon relay ZA is cle-energized.

Relay SS in releasing also opens the circuit of relays HA and HB whichaccordingly fall away. A homing earth through relay RAS is now placed oncontacts 2 to 21 in level P of the secondary distributor S1174 by way ofHA1 and cable G10. The resistance of relay RAS is sufficiently low topermit driving magnet DM4 of secondary distributor S1717'l to energizeover its own interrupter springs IS* andthe switch S1171 is thereforerotated to the A22nd position, For advancing it from position to itshome position earth is supplied through relay RAS, conductor 171 tocontacts 22 to 25 in levelPofsecondarydistributor S117, and the switchS117* is thus rotated to the home position. Contacts 2 to 25 in level Pof all the secondary distributors are multipled together so that anysecondary switches standing oit-normal at this time will be rotated tohome position by the circuits just described.

Relay PL in operating in response to the closure of its circuit asdescribed above at PL2 prepares a circuit for the primary release alarmlamp PRL, Fig. 2, and at PL1 completes a circuit for the two-step relayTAR; earth, PL1, conductor 172, normally closed contacts controlled byarmature 1 of relay TAR, upper winding of relay TAR to battery, and alsocompletes a circuit for the holding coil of the time check relay TG1from battery, lower winding of TG1, conductor 173, cable G14, conductor17 3, Fig. 4, normally closed contacts controlled by armature l, relayTAR, conductor 172, PL1 to earth. Relay TAR at this time only operatesits contacts TAR, whereupon a circuit is closed from the pulse conductorPG, cable G21, conductor 174, PL3, TAR3, TAR, conduetor 175, cable G14,conductor 175, Fig. 2, upper winding of time check relay TG1, resistance176 to battery. Earth pulses are now delivered to the stepping magnet ofthe time check relay TG1 at the rate of one pulse every two seconds.117hen the time check relay operates in known manner, earth is extendedto the lower winding of relay TAR to eiiect its full operation: battery,lower winding of relay TAR, conductor 177, cable G11, conductor 177,Fig. 2, TG3 to earth. Re-

